The use of mobile communications networks has increased over the last decade. Operators of the mobile communications networks have increased the number of base stations in order to meet an increased demand for service by users of the mobile communications networks. The operators of the mobile communications networks wish to reduce the running costs of the base station. One option to do this is to implement a radio system as an antenna-embedded radio forming an active antenna array. Many of the components of the antenna-embedded radio may be implemented in one or more chips.
Nowadays active antenna arrays are used in the field of mobile communications systems in order to reduce power transmitted to a handset of a customer and thereby increase the efficiency of the base station, i.e. the radio station. The radio station typically comprises a plurality of antenna elements, i.e. an antenna array adapted for transceiving a payload signal. Typically the radio station comprises a plurality of transmit paths and receive paths. Each of the transmit paths and receive paths are terminated by one of the antenna elements. The plurality of the antenna elements used in the radio station typically allows the steering of a beam transmitted by the antenna array. The steering of the beam includes but is not limited to at least one of: detection of direction of arrival (DOA), beam forming, down tilting and beam diversity. These techniques of beam steering are well-known in the art.
The code sharing and time division strategies as well as the beam steering rely on the radio station and the antenna array to transmit and receive within well defined limits set by communication standards. The communications standards typically provide a plurality of channels or frequency bands useable for an uplink communication from the handset to the radio station as well as for a downlink communication from the radio station to the handset. In order to comply with the communication standards it is of interest to reduce so called out of band emissions, i.e. transmission out of a communication frequency band or channel as defined by the communication standards.
For example, the communication standard “Global System for Mobile Communications (GSM)” for mobile communications uses different frequencies in different regions. In North America, GSM operates on the primary mobile communication bands 850 MHz and 1900 MHz. In Europe, Middle East and Asia most of the providers use 900 MHz and 1800 MHz bands.
Digital dividend spectrum auctions and other releases of frequency spectrum have led to the desire from operators for multi-band products. Multi-band products save space on masts and hence save site rental and installation costs. The multi-band products may also enable two bands to be accommodated on heavily used masts where no space exists for additional antennas.
The multi-band products are conventionally implemented by providing a plurality of remote individual transceivers and a separate diplexer. Each one of the plurality of transceivers corresponding to an individual band of the plurality of communications bands.
FIG. 1 shows a conventional dual-band transceiver 1′ based on two individual band transceivers 1A, 1B. A digital signal processor (DSP) 15′ receives and processes a transmit digital signal 2000. The digital signal processor (DSP) 15′ also receives and processes a receive digital signal 2100.
The individual band transceiver 1A comprises a transmit path 1000-1A carrying a transmit signal 2000-1A and a receive path 1100-1A carrying a receive signal 2100-1A. The individual band transceiver 1B comprises a transmit path 1000-2B carrying a transmit signal 2000-2B and a receive path 1100-2B carrying a receive signal 2100-2B.
The transmit signal 2000-1A comprises signals of frequencies in a first transmit band frequency TB1. The transmit signal 2000-2B comprises signal of frequencies in a second transmit frequency band TB2. Similarly, the receive signal 2100-1A comprises signals of frequencies in a first receive frequency band RB1. The receive signal 2100-2B comprises signals of frequency in a second receive frequency band RB2.
Each of the transmit paths 1000-1A, 1000-2B comprises a digital-to-analogue conversion and upconversion block 2-1, 2-2, a first filter 3-1, 3-2, and a radio frequency amplifier 4-1, 4-2.
The transmit signal 2000-1A, 2000-2B is converted into an analogue form and up-converted to radio frequency by the digital-to-analogue conversion and upconversion block 2-1, 2-2. The first filter 3-1, 3-2 is adapted for passing the transmit frequency band TB1, TB2 and to remove unwanted products from the digital-to-analogue conversion process. The output of the first filter 3-1, 3-2 is passed to a radio frequency amplifier 4-1, 4-2.
The output of the amplifier 4-1 on the transmit path 1000-1A is passed to a duplexer 5-1. The duplexer 5-1 is adapted to appropriately separate the analogue transmit signal 2000-1A leaving the amplifier 5-1 and the analogue receive signals 2100-1A for their specific bands TB1, RB1.
The output of the amplifier 4-2 on the transmit path 1000-2B is passed to a duplexer 5-2. The duplexer 5-2 is adapted to appropriately separate the analogue transmit signal 2000-2B leaving the amplifier 5-2 and the analogue receive signals 2100-2B for their specific communications bands TB2, RB2.
The output of duplexer 5-1, 5-2 in the transmit path 1000-1A, 1000-2B corresponds to the radio frequency output of the transceiver 1A, 1B. The output of the duplexer 5-1, 5-2 feeds a diplex filter 6, which separates the transmit signal 2000-1A carrying the transmit frequency band TB1 and the transmit signal 2000-1A carrying the transmit frequency band TB2. This allows the two transceivers 1A and 1B to operate independently of each other.
The diplex filter 6 receives the receive signal 2100-1A, 2100-2B of the multi-band transceiver. The receive signal 2100-1A carries the receive frequency band RB1, and the receive signal 2100-2B carries the receive frequency band RB2.
The diplex filter 6 feeds the duplexers 5-1, 5-2 in the receive paths 1100-1A, 1100-2B, respectively. The receive signal 2200-1A, 2200-2B leaving the duplexer 5-1, 5-2 in the receive paths 1100-1A, 1100-2B is passed to a low noise amplifier 8-1, 8-2.
After amplification, the receive signal 2200-1A, 2200-2B is passed to a filter arrangement 9-1, 9-2 followed by an analogue-to-digital conversion and downconversion block 10-1, 10-2.
The filter arrangement 9-1 is adapted for passing the receive frequency band RB1 of the received signal 2200-1A on the individual one of the receive paths 1100-1A. The filter arrangement 9-2 is adapted for passing the receive frequency band RB2 of the received signal 2200-2B on the individual one of the receive paths 1100-1B.
This dual band transceiver as described in FIG. 1 is however both expensive and inefficient. The diplex filter needs to be of high power, which makes the diplex filter expensive. The diplexer also introduces losses that come on top of the duplexer losses already present in each of the individual band transceivers 1A, 1B. This in turn reduces the output power, the system efficiency and increases the receiver noise figure. All of these have an undesirable impact upon system performance.
Additionally, in the case of an active antenna system, the very tight space and cost requirements would increase the loss in this diplexer significantly, hence making this conventional solution very unattractive.
An alternative conventional dual-band transceiver is shown on FIG. 2. The alternative dual-band transceiver differs from the dual-band transceiver of FIG. 1 in that the two duplexers 5-1, 5-2 and the diplexer 6 are replaced by a quadruplexer 7.
The use of the quadruplexer 7 instead of the two duplexers 5-1, 5-2 and the diplexer 6 overcomes much of the additional loss introduced by the diplexer 6. However, the alternative conventional dual-band transceiver of FIG. 2 is still very large and expensive, due, primarily, to the size and cost of the quadruplexer.